Device for controlling valve kinematics

ABSTRACT

A device for controlling the variation of the opening and closing times and durations of a valve ( 8 ) comprises an elastic means ( 18 ) acting upon an assembly consisting of a lever device ( 1 ) and a valve stem ( 11 ) not in the closing direction but in the opening direction of the valve ( 8 ). The assembly consisting of the lever device ( 1 ) and of the opening cam ( 5 ) and the closing cam ( 6 ) fulfils a dual function, one for opening the valve ( 8 ), the other for moving it back for its closure. The control device, which comprises a device for offsetting the angular position of the cam position relative to the crankshaft, allows to control the opening and closing duration of the valve ( 8 ) over a very wide range extending, for opening, from 210° to 350° of crankshaft rotation approximately, by varying the valve opening and closing times independently of each other. It is applicable to a wide range of engines.

[0001] The present invention relates to a device for controlling thekinematics of at least one valve according to the preamble of claim 1.

[0002] The variable control of valves, i.e. variable timing, is acomplex problem that has often been approached. According to severalrecent studies, the majority of the systems suggested up to now comprisea limited variability of opening durations or do not offer a progressivevariation of the opening durations. Certain electro-hydraulic systemsoffer a higher flexibility of the opening duration, but they suffer fromthe disadvantage of being very complex and are subject to technicalproblems that are difficult to solve, such as delays and thecompressibility in the hydraulic circuits as well as the spaceconsumption of their components.

[0003] Based on this state of the art, it is an object of the presentinvention to propose a control device as cited above which allows tocontrol the opening and closing duration of the valve over a wide range(comprised, for the opening, between 210° and 350° of camshaft rotationapproximately), while varying the opening and closing times of thevalve(s) independently of each other. The implementation of this devicemay be provided for a wide range of engines. This object is attained bythe means defined in claim 1. Advantageous realizations are described inthe dependent claims.

[0004] Embodiments of the invention will be described by way ofnon-limiting examples hereinafter with reference to the encloseddrawings where:

[0005]FIG. 1 schematically shows a first embodiment of a device of theinvention with the valve in the closed position,

[0006]FIG. 2 shows the device of FIG. 1 with the valve in the closedposition,

[0007]FIG. 3 shows a second embodiment of a device of the invention withthe valve in the closed position, and

[0008]FIG. 4 shows the device of FIG. 3 with the valve in the openposition,

[0009]FIG. 5 shows an angular offset control for the cams of FIGS. 1 to4,

[0010]FIG. 6 shows a third embodiment of a device of the invention withthe valve in the closed position,

[0011]FIG. 7 shows the device of FIG. 6 with the valve in the openposition,

[0012]FIG. 8 schematically shows the operation of the device and thesuperposed adjustment of the cams for a short opening, and

[0013]FIG. 9 schematically shows the superposed adjustment of the camsof FIG. 8 for a long opening.

[0014]FIGS. 1 and 2 refer to an engine with a cylinder head comprisingtwo valves and two common camshafts for intake and exhaust. A rocker arm1 with its two sliders 2, 3 pivoting around its shaft 4 is controlled bytwo cams, namely an opening cam 5 and a closing cam 6, the two camsrotating in opposite directions, as indicated by arrows 5F, 6F. Rockerarm 1 further comprises a fork 7 for controlling valve 8, shown in theclosed position in FIG. 1 and in the open position in FIG. 2.

[0015] Opening cam 5 includes three distinct geometrical portions: afirst concentric portion Y-A (corresponding to the retention of valve 8against its seat 10 and to the takeover of rocker arm 1 during theclosed valve phase (large radius R2 of the cam)), a second eccentricportion A-B (causing the opening movement of the valve), and a thirdconcentric portion B-L (small radius R1 of the cam).

[0016] In analogy, closing cam 6 comprises a first concentric portionK-B′ (zone of takeover of rocker arm 1 during the open phase of valve 8(small radius R3 of the cam)), a second eccentric portion B′-C (causingthe closing movement of the valve), and a third concentric portion C-X,corresponding to the retention of valve 8 against its seat 10 (smallradius R4 of the cam).

[0017] Valve 8 is provided at its lower end with a tulip 9 adapted topress against a seat 10, the tulip being followed by a stem 11 that isguided by a valve stem guide 12 and fastened by means of a lockingdevice comprising a valve spring seat 13 cooperating with a circularclip 14 and sliding in a tubular valve retainer 15 whose upper part isfitted with a locking ring 16 allowing the closure of a non-referencedvalve retainer chamber. Locking ring 16 is provided with a threaded borefor receiving an adjusting pin 16G for adjusting the initial tension ofa spring 17 adapted to act upon stem 11 of the valve (through elements13, 14).

[0018] This damping spring 17 is accommodated in the space formedbetween the bottom of valve retainer 15 and valve spring seat 13. Thefunction of this damping spring is easily understood when comparingFIGS. 1 and 2 and reading the discussion of the operation of the device(see below, point 10 of the present disclosure).

[0019] Inversely to valve controls of the prior art, an elastic memberacting upon valve 8 and rocker arm 1 is formed of a valve relievingspring 18. The latter tends to open the valve and allows the rocker arm,which retains the valve through valve retainer 15, damping spring 17 andlocking device 13, 14, to follow the profile of the cams. Spring 18 ismaintained by an upper spring seat 19, on one hand, and on the otherhand, by a circular shoulder 20 formed around valve retainer 15.

[0020]FIGS. 3 and 4 show a variable timing system for an engine with afour-valve cylinder head with valve 8 in the closed and in the openposition, respectively. One rocker arm 21 is common to two valves andpivots around a shaft 22. The rocker arm comprises an arm 23 carrying acontact member 24 (e.g. a roller bearing or, as in the illustratedembodiment, a slider), a slider 24 and a fork 25 for actuating valve 8.Opening cam 5 acts upon slider 24 of the arm of the rocker arm, whereasclosing cam 6 acts upon a roller bearing 26 turning on an axle 27mounted on the arm of the rocker arm provided with fork 25.

[0021] In this embodiment for four valves per cylinder, the rocker armis not actuated by a spring that is positioned in the axis of the valvestem but by a detent spring 28 one shank of which rests on a stop 29while the other shank rests on a stop 30. The arrangement of the rockerarm is such that detent spring 28 tends to open the valve, asillustrated in FIG. 4. This embodiment (common rocker arm for twovalves) may also be conceived with the detent and damping systemsdescribed with reference to FIGS. 1-2 and 6-7.

[0022] The stem, retainer, guide, and seat of the valve are similar tothose of the preceding embodiment, as well as the damping system withdamping spring 31, which is retained between a sleeve or threaded ring16B closing a non-referenced chamber of a support 32 and sliding on thevalve extension rod 57 with threaded end, on one hand, and a support nut33 that is blocked by a counternut 34. Valve stem 11 and extension rod57 are assembled by means of a coupling sleeve 35 that is retainedbetween two counternuts 36.

[0023]FIG. 5 shows a device for offsetting the angular position of thecamshafts relative to the crankshaft, the device being known per se.Opening cam 5 and closing cam 6 are shown in cross-section and in frontview, the cams being the same as those described above. Cam 5 isfastened on opening camshaft 37 and cam 6 on closing camshaft 38, thecamshafts being guided by respective bearings 39, 40. Sleeves 41, 42,provided with helicoidal internal grooves 43, 44 and comprising drivinggears 45, 46 of the camshafts are fastened by dowel pins 47 of the gearson the shaft.

[0024] Camshaft 38 is provided with a toothed pinion 48 that is chaindriven by the crankshaft, the pinion being connected to driving gears 46by fastening means 49.

[0025] Control pieces 50 and 51 are fitted on a distance over the endsof the camshafts. The ends comprise an internal coupling by straightspline 52, 53 and an external coupling by helicoidal grooves 43, 44.

[0026] In order to effect the mutual angular offset of cams 5, 6, one orthe other of the control pieces (50, 51), or both, are slidinglydisplaced to obtain a shorter or longer valve opening duration.

[0027] This control device is also applicable in other timing gearsystems, e.g. with finger control or with direct actuation.

[0028]FIGS. 6 and 7 show an embodiment for a cylinder head with two orfour valves where cams 5 and 6 are arranged on a single camshaft (seealso FIGS. 8 and 9). Valve 8 and its attachment as well as the elasticdetent and damping members correspond to those of FIGS. 1 and 2.

[0029] Rocker arm 54, oscillating around its shaft 55, is similar to theone illustrated in FIGS. 3 and 4 and comprises two sliders 56 of whichonly one is visible in the drawing, but it is understood that thecontrol of the angular offset will have to be adapted correspondingly.

[0030]FIGS. 8 and 9 schematically show the operation and the adjustmentof the superimposed combination of the opening cam and the closing cam,the cams being adjusted to result in a short opening of the valve. Thepositions of the cams for a desired opening duration of the valve areillustrated, where A is the starting point of the opening, B1, B are thepoints between which the valve is maximally open, and C is the closureend point.

[0031] According to the example illustrated in FIG. 8, the valve isclosed on 240° and open on 120°. The arc X-Y represents minimum crossingof the cams when the latter are adjusted to the position of shortopening of the valve.

[0032] In FIG. 9, the opening cam is angularly offset by 30° in itsrotating direction and the closing cam is angularly offset by 30° in theopposite direction of its rotation. By these angular offsets, theopening time of the valve is shifted to 1800 (respective angles beingexpressed in degrees of cam rotation).

[0033] It follows that in a general manner, and conversely to thetraditional devices of the prior art, the elastic detent means 18, 28acts upon the pair [lever device (1; 21; 54)-valve stem (11)] in theopening direction of the valve (8), whereas the pair [rocker armdevice—opening cam 5/closing cam 6] fulfills a double function, namelyto allow the opening of the valve and to move it back to its seat 10 forits closure. Based on this original conception as described above, theoperating mode may be demonstrated as follows (see particularly FIGS.1-2 and 8-9):

[0034] 1. The end of the phase in which valve 8 is closed is ensured bythe cam surface corresponding to the profile A-Y of opening cam 5.

[0035] 2. The opening phase starts when slider 2 has passed point A ofcam 5.

[0036] 3. Valve detent spring 18 expands and enables slider 2 to followthe eccentric profile A-B.

[0037] 4. From the moment when slider 2 passes point A, and over about8° of rotation of cam 5, the valve remains closed and damping device 17expands to its initial position (see point 10 below and FIG. 1).

[0038] 5. From the instant when this initial position is attained, themovement of cam 5 on rocker arm 1 causes the valve to be lifted from itsseat 10.

[0039] 6. When slider 2 arrives at point B of cam 5, slider 3simultaneously contacts concentric surface K-B′ of closing cam 6 whichactuates rocker arm 1 during the closing phase. The valve is nowmaximally open (see FIG. 2).

[0040] 7. The closing movement of the valve and the compression ofdetent spring 18 start when slider 3 arrives at point B′ of cam 6 andcontinue until the slider arrives at point C.

[0041] 8. For a short opening of the valve, e.g. during 210° ofcrankshaft rotation, slider 3 contacts surface K-B′ exactly at point B′,and as points B and B′ coincide, the valve immediately starts to closeagain.

[0042] 9. For a longer opening up to 350° of crankshaft rotation, threesolutions are possible:

[0043] A) either an angular offset of the closing camshaft contrary tothe rotational direction, thereby retarding B′-C and thus the closingmovement by increasing the distance between B′ and B by means of theangular offsetting device.

[0044] B) or an angular offset of the opening camshaft in the rotationaldirection, thereby advancing A-B and thus the opening movement byincreasing the distance between B and B′ by means of the angularoffsetting device of the opening camshaft.

[0045] C) or the simultaneous application of the two possibilities.

[0046] In all three cases, the valve remains maximally open during thetime in which slider 3 moves from B to B′.

[0047] 10. The valve contacts its seat 10 about 80 before slider 3reaches point C. Damping device 17 is compressed—retainer 15 slidingvalve spring seat 13 on stem 11—and compensates the rest of the liftingmovement imparted by cam 6 during the entire duration of the valveclosure.

[0048] 11. The valve closure phase is divided into two stages. In afirst stage, the valve is kept closed and detent spring 18 compressed bythe action of surface C-X of cam 6 on slider 3.

[0049] 12. During this action, slider 3 is in waiting position for theflush passage of point Y of cam 5, which marks the second stage.

[0050] 13. From then on, rocker arm 1 is taken over by surface A-Y ofcam 1 at least 5° of cam rotation before slider 3 arrives at X (in orderto ensure a minimum cam crossing XY in the case of a short valveopening).

[0051] 14. Thus, the transition from one cam to the other is free ofshocks, and the cycle may start again.

[0052] The fact that the drives of the opening and of the closingcamshafts are provided with an angular offsetting device with helicoidalgrooves, on one hand, and that the profiles of the cams are inagreement, on the other hand, allows to vary the opening and the closingtime of the valve independently of each other. Furthermore, the dampingdevice ensures tightness between the seat and the valve without shocksin the timing gear and compensates for the lengthening of the valve dueto thermal dilatation.

[0053] The cams can be mounted on their shafts in different ways and maybe rotationally driven in the same direction. It is also possible toprovide a respective shaft for each cam or a common shaft or commonshafts.

[0054] Thanks to the original cam profiles, it is possible to obtainshort (FIG. 8) or long opening durations (FIG. 9) or any otheropening/closing durations between the extremes. Thus, in practice, thedevice operates as a “variable cam”, figuratively speaking.

1. Device for controlling the kinematics of at least one valve, thedevice comprising at least one opening cam and one closing cam, and atleast one lever device cooperating with the valve and subject, togetherwith the latter, to the action of an elastic member, characterized inthat the elastic member constitutes a detent means (18; 28) acting uponthe assembly composed of the lever device (1; 21; 54) and of the stem(11) of the valve (8) in the opening direction of the valve, and in thatthe assembly comprising the lever (1; 21; 54) and the cam (5,6) allowsthe opening of the valve (8) and furthermore generates the returnmovement of the valve onto its seat (10) for its closure.
 2. Deviceaccording to claim 1, characterized in that the opening cam (5)comprises a first concentric portion (Y-A) corresponding to a radius(R2) of the cam, a second eccentric portion (A-B), and a thirdconcentric portion (B-L) corresponding to a radius (R1) of the cam, R2being larger than R1, and in that the closing cam (6) analogouslycomprises a first concentric portion (K-B′) corresponding to a radius(R3) of the cam, a second eccentric portion (B′-C), and a thirdconcentric portion (C-X) corresponding to a radius (R4) of the cam, R4being larger than R3.
 3. Device according to claim 1 or 2, characterizedin that the detent means is a spring (18) acting upon the stem (11) ofthe valve (8).
 4. Device according to claim 1 or 2, characterized inthat the detent means is a detent spring (28) winding around the axle(22) and acting upon an arm of the lever (21).
 5. Device according toone of claims 1 to 4, characterized in that the attachment of the stem(11) to the valve (8) comprises a damping means (17; 31).
 6. Deviceaccording to claim 5, characterized in that the damping means is aspring (17) accommodated in a valve retainer (15) mounted on the stem(11) of the valve (8).
 7. Device according to claim 6, characterized inthat the chamber of the valve retainer (15) is closed by a nut (16)comprising an adjusting pin (16G) for adjusting the initial tension ofthe damping spring (17-31).
 8. Device according to claim 5,characterized in that the damping means comprises a damping spring (31)accommodated between two supports (32, 33), support 32 sliding on anextension rod (57) of the valve (8).
 9. Device according to one ofclaims 1 to 8 comprising a respective camshaft (37, 38) for each cam (5,6), characterized in that the lever is a rocker arm (1) comprising twoslider support arms (2, 3) actuated by the cams (5, 6) and a fork (7)acting upon the stem (11) of the valve.
 10. Device according to one ofclaims 1 to 8 comprising a respective camshaft (37, 38) for each cam (5,6), characterized in that the lever is a rocker arm (21) comprising aslider support arm (24) and a fork arm (25) acting upon the stem (11) ofthe valve, the fork further comprising a roller bearing (27), and thecams (5, 6) acting upon the slider and the roller bearing.
 11. Deviceaccording to one of claims 1 to 10 comprising a respective camshaft (37,38) for each cam (5, 6), characterized in that the angular offsettingdevice comprises a control piece (50, 51) for each camshaft (37, 38),the control piece, sliding on the camshaft, being provided with astraight spline coupling (52, 53) and with a coupling by means ofhelicoidal grooves (43, 44).
 12. Device according to claim 10,characterized in that the offsetting control further comprises drivinggears (45, 46) for the camshafts that are actuated by a toothed pinion(48) driven by a chain from the crankshaft.
 13. Device according to oneof claims 1 to 7 comprising opening (5) and closing (6) cams fastened onthe same camshaft, characterized in that the lever is a rocker arm (54)comprising two sliders (56) actuated by the cams (5, 6), the rocker armfurther comprising a fork (7) acting upon the valve stem (11).